Mavjee, Vijay The afternoon pressure for sleep Halfway through the waking period, around early afternoon, there is a strong propensity for sleep to occur again. This second sleep tendency is part of a 12-hour rhythm of sleepiness, that I have termed "The Afternoon Pressure for Sleep" (APS). Evidence for this bicircadian sleepiness, include siesta cultures, short sleep latencies in the afternoon, a midday peak in pathological sleep attacks, and the concentration of napping to this afternoon window. The flexible nature of the human sleep/wake cycle allows for napping to be easily suppressed, as necessitated by social and occupational demands, and so the APS is readily masked. [Continues.] untagged;Medical and Health Sciences not elsewhere classified 2017-10-25
    https://repository.lboro.ac.uk/articles/thesis/The_afternoon_pressure_for_sleep/9610298